1. Field of Invention
The present invention relates to a device for measuring a seat load, including measuring the load of an object placed on a passenger seat or the like.
2. Description of the Related Art
An automobile is provided with a seat belt or an air bag as equipment for securing the safety of the passenger. Recently, to further improve the performance of the seat belt or the air bag, there is the possibility to control the operation of such safety equipment in accordance with the weight and attitude of the passenger. For example, the amount of gas generated for the air bag or the amount of pre-tension created for the seat belt is adjusted in accordance with the weight and attitude of the passenger. For these purposes, it is necessary to know by some way the weight of the passenger sitting on the seat. Further, to assume the attitude of the passenger, the position of the center of gravity of the passenger on the seat needs to be known as well.
As an example of the means for knowing the weight and the center of gravity of the passenger, Japanese Unexamined Patent Application Publications No. 11-1153 and 11-30457 disclose a method according to which the seat weight including the weight of the passenger is measured by obtaining the sum total of the vertical loads applied to a load cell. With this method, it is also possible to know the position of the center of gravity of the passenger on the seat.
Such a seat weight measuring device must be as inexpensive as possible because it is mounted in an ordinary automobile. Further, the wiring, assembly, etc. of the device must also be of a simple design. Additionally, to perform the correct measurements, it is desired to prevent as much as possible a weight other than the weight of the passenger (or an object) on the seat from being applied to the sensor.
The present invention has been made in view of the above problems. It is accordingly an object of the present invention to provide a seat weight which makes it possible in a seat of the type which supports the seat load at three points to reduce the production/assembly cost and to measure the weight of the person on the seat more correctly.
As a first embodiment for solving the above problems, there is provided a seat load measuring device for measuring the load of a seat of a passenger vehicle (including the load of an object placed on the seat), wherein the load of the seat is received at three positions, the load being put together in a single load cell and transmitted through a transmission mechanism, load measurement being performed by the single load cell.
In the seat to which the present invention is applied, the seat load is supported at three positions (usually a one front central position and rear right and left positions). Thus, in this means, the seat load is received at three positions corresponding to these support portions. And, by means of the load transmission mechanism, these loads are put together into a single load cell for transmission, the entire seat load being measured by the single load cell. Thus, a single load cell suffices, which reads to a reduction in cost since a measurement circuit, wiring, etc. are omitted.
As a second embodiment for solving the above problems, there is provided a seat load measuring device for measuring the load of a seat of a passenger vehicle (including the load of an object placed on the seat), wherein the load of the seat is received at three positions, the load being transmitted to a single load measurement plate to which a strain gauge is mounted through a transmission mechanism to perform load measurement, the strain gauge being mounted to the load measurement plate such that the strain gauge is capable of independently measuring the load of at least one of the three positions.
In this embodiment, the method of receiving the seat load is the same as the first means. However, the load measurement device is not a single load cell but a single load measurement plate. A load received at three points is transmitted to this load measurement plate through a load transmission mechanism. A strain gauge is mounted to the load measurement plate such that the load of at least one of the three positions can be independently measured. Thus, with this means, it is possible to independently measure the load of three positions, making it possible to measure the position of the center of gravity.
As a third embodiment for solving the above problems, there is provided a seat load measuring device which is the above-mentioned first or second means, wherein the transmission mechanism includes a lever mechanism rotating around a horizontally oriented axis, receiving the load of the seat at the force point portion of the lever mechanism and transmitting the load to the load cell or the load measurement plate at the point of application, a deflection mechanism being provided between the rotation axis and the point of application.
In this embodiment, the load is transmitted through the lever mechanisms (in the case of the first means, two or three lever mechanisms, and in the case of the second means, three lever mechanisms), a deflection mechanism being provided between the rotation axis (fulcrum) and the point of application of this lever mechanism. Thus, when a seat load is applied to the force point portion, the lever transmits the load to the load cell or the load measurement plate as it is deflected by the deflection mechanism portion. Thus, even when there is a play in the load measurement mechanism and the seat support portion in front of it, the play is absorbed by this deflection mechanism, so that it is possible to prevent the measurement value becoming incorrect due to the play and, at the same time, to facilitate the assembly.
As a fourth embodiment for solving the above problems, there is provided a seat load measuring device which is one of the first through third means, wherein a play which permits positional deviation of the point of application generated due to deflection of the lever is provided in the joint portion of the point-of-application portion of the lever and the load cell or the load measurement plate.
In the above third embodiment, when the lever is deflected in the deflection portion, the horizontal length changes slightly. In this means, a play which absorbs such a variation in length is provided in the joint portion of the point-of-application portion of the lever and the load cell or the load measurement plate, so that if this is generated, no stress is generated, and the load measurement is not made incorrect by such stress. By providing such a play in the means other than the third means, the assembly is facilitated.
As a fifth embodiment for solving the above problems, there is provided a seat load measuring device which is one of the first through fourth embodiments, wherein a vertical play is provided in the joint portion of the point-of-application portion of the lever and the load cell or the load measurement plate.
In this embodiment, a vertical play is provided in the joint portion of the point-of-application portion of the lever and the load cell or the load measurement plate, so that even when there is a play in the load measurement mechanism or the seat supporting portion in front of it, such a play is absorbed by the play provided in the joint portion of the point-of-application portion of the lever and the load cell or the load measurement plate, whereby it is possible to prevent the measurement value from being made incorrect due to the play and, at the same time, the assembly is facilitated.
As a sixth embodiment for solving the above problems, there is provided a seat load measuring device which is one of the first through fifth embodiment, wherein a mechanism for preventing a load larger than a predetermined load from being transmitted to the load cell or the load measurement plate is provided in the portion receiving the seat load.
In this means, a mechanism for preventing a load larger than a predetermined load from being transmitted to the load cell or the load measurement plate when a load larger than a predetermined load is applied to the portion receiving the seat load (the force point portion) is provided in the portion receiving the seat load (the force point portion). Thus, it is possible to prevent the load cell or the load measurement plate from being damage under a load larger than a predetermined load or prevent the measurement from being performed in an abnormal manner.